Portal 2 - Xbox 360

What We Know: The folks at Valve were genuinely surprised when their quirky, mind-bending, puzzle shooter Portal became a smash hit when it was released as part of the Orange Box back in 2007. It’s hard to imagine Valve being surprised with success, but by their own admission, they just weren’t sure if gamers would embrace it. So when it came time to start thinking about Portal 2, Valve decided to take everything that players loved about the first game, and build it out into a standalone title that not only expands the gameplay into tons of challenging and varied ways, but that delivers a more complex and deep narrative experience that picks up “several lifetimes” after the first game.

What We're Seeing Now: The developers at Valve noticed something peculiar when people started playing Portal: Although the game is single-player, gamers converted it into a two-player game, with one dude driving and another offering helpful suggestions. Sequel to the rescue: Portal 2 will feature built in co-op. The PS3 and 360 versions will feature both online and couch-based, two-player action.

At PAX 2010 this year, I was lucky enough to try out the co-op during Valve's demo of the new mode. My palms were sweating a bit. I'm not use to gaming in front of an audience, and I didn't want to make G4 look bad. Luckily, Portal 2 controls pretty much like Portal -- left button shoots one portal, right button shoots the other -- so gameplay wise,  I was straight.

The demo at PAX showed off the beginning of the game's two-player track. It's totally separate from single-player, and Valve says it's about twice as long as the entirety of Portal. A key difference from the first game are the characters. Chell is saved for the single-player experience. In co-op, players take the role of either a skinny, orange robot or a fat, blue one. Each has a portal gun, and the two work together to solve challenges presented by GLADos.

The combination of a fat one and a skinny one has been a comedy staple since Laurel and Hardy, and it works here, too. The addition of gestures helps. Some are contextual, and some, like waving or hugs, can be done any time. More games need hug buttons -- watching the two mechanical pals hug it out is hysterical and touching.

An equally funny element: GLADos. Apparently, the close relationship of the two robots troubles the manic-depressive AI, as she spends the game seemingly trying to drive a wedge between them. Although there's no real competitive element to the gameplay, GLADos loves pointing out how much better one robot did on a test over the other.

Because there are twice as many portals at play in Portal 2, as well as new gameplay elements like propulsion gel, repulsion gel, and the newly-introduced light bridges, the puzzles have the potential of being exponentially more complex as the first game. The first couple puzzles in the demo were simple, but definitely hinted at the possibilities coming in the full game. For example, you can jump in an infinity fall portal combination, then have your partner rocket you out with great force -- in the case of the demo, across a great chasm of goo.

A new puzzle element introduced at PAX is the light bridge. It's basically a beam of light you walk on, so it's possible to direct it through portals, and light your way to the exit.

Overall, the co-op demo had that most enviable of video game problems: It was too short. I played the game for around 15 minutes, and could easily have sat there for 15 hours. The addition of another player to Portal 2's first-person puzzling is a pure joy, if for no other reason than the ability to say "Did you see that?" and know the answer is "Yes."

Portal 2 comes out on the PC, Mac, PS3 and 360 on February 9.